1. Field of the Invention
The present invention relates generally to the field of signal processing systems for use in parametric sound reproduction.
2. Related Art
A parametric array in air results from the introduction of sufficiently intense, audio modulated ultrasonic signals into an air column. Self demodulation, or down-conversion, occurs along the air column resulting in an audible acoustic signal. This process occurs because of the known physical principle that when two sound waves with different frequencies are radiated simultaneously in the same medium, a modulated waveform including the sum and difference of the two frequencies is produced by the non-linear interaction (parametric interaction) of the two sound waves. When the two original sound waves are ultrasonic waves and the difference between them is selected to be an audio frequency, an audible sound is generated by the parametric interaction.
While the theory of parametric sound production has been addressed in numerous publications, commercial attempts to capitalize on this intriguing phenomenon have largely failed. Most of these efforts have proved unsuccessful because many of the basic concepts integral to such technology while, relatively easy to produce and operate in laboratory conditions, have not scaled properly in applications where relatively high (or even useful) volume output is necessary. As these technologies have been scaled to commercial levels, distortion of parametrically produced sound output results in undesirable systems.
Certain specific problems continue to arise when the emitter at issue utilizes a PVDF film. Such films typically stretch or contract in reaction to changing environmental conditions such as heat, humidity, etc. (either solely as a result of exterior, environmental conditions, or as a result of operation of the emitter, or both). This geometric change in the emitter film can result in poor performance of the emitter, or can result in damage being done to the film (and/or other components of the emitter).